Abstract:

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We report the results of a SIMS and micro-Raman investigation performed on cubic (3C)
SiC crystals grown on hexagonal SiC seeds using a Ge-Si bath and the so-called Vapor Liquid Solid
growth technique. From SIMS measurements, we find a Ge concentration which, roughly, scales
like the Ge concentration in the melt and, in term of micro-Raman measurements, explains the
presence of weak but discernable Ge-Ge peaks around 300 cm-1. Since no similar Si-Si vibrations
are found, this discard the possibility of having at the same time both Ge and Si constitutional
super-cooling with two separate Ge and Si phases.

Abstract: Acetylene and ethylene are frequently used in vacuum carburizing in Japan. In this study
the natural gas which is available from the lifeline is applied to vacuum carburizing. The gas
composition inside the furnace was analyzed by the gas chromatography in order to examine the
carbon infiltration mechanism. Unsaturated hydrocarbon gases (such as acetylene and ethylene) are
generated from the natural gas. The effect of acetylene concentration in the furnace on the carbon
infiltration rate was investigated. The carbon amount which infiltrates into the steel increases, as
acetylene concentration in furnace increases. It is possible that carbon concentration of specimen
surface increases to the cementite precipitation concentration in the short term, when natural gas
flow rate increases in the initial carburizing stage. After that, carbon concentration of specimen
surface does not decrease, even if the natural gas flow decreases, because carbon atoms which are
consumed for diffusion to inside are sufficiently supplied. By using this method, inhibition of soot
generation, reduction of process gas and shortening of the carburizing period are possible. The
carbon concentration profile of the vacuum carburized specimen was compared with the simulation.

Abstract: Porous C/C composite with certain porosity prepared by Chemical vapor infiltration
(CVI) was chosen as the preforms to develop the C/C-SiC composites through precursor infiltration
and pyrolysis(PIP), using PCS (polycarbosilane) as the precursor and divinylbenzene as solvent and
cross-linking reagent for PCS. The effect of the infiltration solution with different PCS/DVB ratio on
the final density, microstructure, and mechanical properties of composites was investigated and the
proper PCS/DVB ratio to prepare the C/C-SiC composites was suggested. The experimental results
showed that the final densities and the mechanical properties of the composites were close related to
the PCS/DVB ratio. Higher PCS/DVB ratio resulted in higher final density and better mechanical
properties, but not the highest PCS/DVB ratio could get the best mechanical properties. The main
reason is that too high PCS/DVB ratio will make the infiltration process become difficult and lead to
the formation of lots of pores in the final composite, at last lowers the mechanical properties. It is
believed that the 50% PCS content is proper to prepare the C/C-SiC composites. The composite from
50% PCS infiltration solution could get the final density of1.696g/cm3, the flexural strength of
171Mpa, and shearing strength of 21.6Mpa, which are the best mechanical results among the obtained
materials.

Abstract: The efficiency of solar cells produced from crystalline silicon materials is considerably
affected by the presence of metal impurities. In order to reduce the concentration of metal
impurities, gettering processes as phosphorus diffusion gettering (PDG) and aluminum gettering
(AlG) are routinely included in solar cell processing. Further development and optimization of
gettering schemes has to ground on physics-based simulations of gettering processes.
In this contribution we use quantitative simulations to compare the efficiency and kinetics of PDG
and AlG in the presence of precipitates for interstitially dissolved metals, like iron, at different
gettering conditions. Recently measured segregation coefficients of iron in liquid AlSi with respect
to crystalline silicon are used in order to compare with PDG under typical conditions. It is shown
that kinetics of both, PDG and AlG, can be separated into two regimes: (i) at low temperatures
kinetics are limited by precipitate dissolution, and (ii) at high temperatures kinetics of AlG is
mainly limited by metal impurity diffusion while phosphorus in-diffusion is the limiting factor of
PDG.

Abstract: Cellulose is one of the main components of renewable lignocellulosic biomass. Functional cellooligosaccharides obtained from the hydrolysate of cellulose could be used as model compounds to study the chemical reactivity of cellulose. HPLC, 1H NMR and 13C NMR techniques were used to analyze the degradation products of cellotriose and cellotetraose oxided by hydrogen peroxide. Results demonstrated that the main degradation products were oligosaccharides with lower degree of polymerization (DP), glucose, and other products including polyhydroxy acid and ketone. The degradation rate declined with the increment of DP. The degradation of cellotriose and cellotetraose at 60 °C followed a pseudo-first-order rate law, the degradation reaction rates were k3=0.25 h-1 and k4=0.15 h-1. Cellooligosaccharides could be degraded completely at higher temperature and for longer reaction time. Degradation products were also degraded at higher temperature and for longer time. The concentration of degradation products went up with the increase of substrate concentration.